1. Field of the Invention
The present invention relates to a magnetic recording medium such as a magnetic disc or a magnetic tape, and more particularly, it relates to a magnetic recording medium which has good dispersibility of magnetic powder, electromagnetic conversion properties and durability.
2. Description of the Related Art
Generally, a magnetic recording medium is produced by coating a substrate such as a polyester film with a magnetic paint which comprises magnetic powder, a binder component, an organic solvent and other necessary components, and then drying. It is desired to use a binder component which gives good dispersibility of the magnetic powder, electromagnetic conversion properties, such as high sensitivity of the recording magnetic medium, and good durability.
Many studies of binder resins have been carried out. For example, a functional group such as a phosphate ester group, sulfone group or hydroxyl group was introduced as a vinyl chloride-vinyl acetate copolymer so as to improve the dispersibility of the magnetic powder (cf. Japanese Patent Kokai Publication No. 44227/1982).
Although the binder resin such as the vinyl chloride-vinyl acetate copolymer which has such a functional group achieves good dispersibility of the magnetic powder, it may have poor durability due to a low polymerization degree and poor cross-linking.